In compliance
assessments that analyze compliance with part 191, subpart C of
this chapter, all underground sources of drinking water in the
accessible environment that are expected to be affected by the
disposal system over the regulatory time frame shall be
considered. In determining whether underground
sources of drinking water are expected to be affected by the
disposal system, underground interconnections among bodies of
surface water, groundwater, and underground sources of drinking
water shall be considered.

40 CFR § 194.53
(U.S. Environmental Protection Agency 1996) requires the U.S.
Department of Energy (DOE) to consider, in compliance
assessments, underground sources of drinking water (USDWs) near
the Waste Isolation Pilot Plant (WIPP) and their
interconnections. A USDW is defined in 40 CFR §191.22 (2000) as “an
aquifer or its portion that supplies a public water system, or
contains a sufficient quantity of ground water to do so and (i)
currently supplies drinking water for human consumption or (ii)
contains fewer than 10,000 milligrams per liter (mg/L) of total
dissolved solids.” The groundwater protection
requirements limit releases to the maximum contamination level
(MCL) established in the Safe Drinking Water Act Regulations at
40 CFR Part 141 (2003) as they existed on
January 19, 1994.

The Compliance Certification Application (CCA) (U.S. Department of Energy 1996), Chapter 8.0, discusses the assumptions and approaches used to
consider USDWs and the uncertainty associated with the
analyses. The DOE provided detailed information on the
location and nature of the USDWs, indicated the estimated
concentrations of radionuclides in a hypothetical USDW in the
accessible environment, and showed that the MCLs for
radionuclides will not be exceeded during the regulatory time
period.

In the CCA, the DOE presented an evaluation of
the USDWs near the WIPP that could potentially be affected by the
disposal system over the regulatory time frame. This
information was included in the CCA, Chapter 8.0, Section 8.2, and Appendix USDW, Section USDW.3. Based on the definitions in section 191.22, the DOE identified three
subcriteria to determine whether a water-bearing horizon located
within the WIPP-controlled area would qualify as a USDW:

1.
A minimum pumping rate of five gallons per minute (gpm)

2.
A supply of water at a rate of five gpm for a 40-year period

3.
A maximum of 10,000 mg/L (10,000 parts per million [ppm]) of
total dissolved solids (TDS)

These requirements characterize the capacity and
quality of a public water system. A public water system is
defined in section 191.22 as a system providing piped water for
human consumption to 25 individuals, or one that has at least 15
service connections.

Applying these criteria, the DOE identified the
Culebra Dolomite Member of the Rustler Formation (hereafter
referred to as Culebra), the Dewey Lake Formation, and the Santa
Rosa Formation as potential USDWs. The DOE conducted a
bounding analysis of the contaminants’ concentrations to
assess compliance with 40 CFR Part
191 Subpart C. In this analysis, the DOE assumed 10,000
ppm TDS, which is much less than the observed concentration of
brine derived from the Salado anhydrite marker beds. A USDW
was also assumed to be present at and beyond the WIPP Land
Withdrawal Boundary. The DOE indicated in the CCA, Chapter 8.0, Section 8.3, that the bounding analysis showed that the
resulting radionuclide concentrations in the USDWs would be less
than half the maximum limit specified in Part
141 (the U.S. Environmental Protection Agency’s
[EPA’s] National Primary Drinking Water Standards), and the
dose to a receptor drinking from the USDW would be a factor of 10
less than the individual protection standard.

The DOE believed the assumption that all
contaminants reaching the accessible environment are directly
available to the receptor is not realistic but conservative,
because this results in overestimating potential doses to an
individual. The DOE’s findings indicated that even
with this conservative approach, the estimated potential dose to
an individual was below the Part 191
requirements. The CCA analysis also assumed that all
contaminants reaching the accessible environment were directly
available to the receptor so that the interconnections of
surface, ground, and underground drinking water were all
considered and treated as a single source.

The EPA examined the DOE’s approach and
assumptions associated with the USDW determination in the
CCA. The EPA found the analyses to be well supported and
accurate, including the uncertainty associated with these
analyses. In addition, the EPA assessed all possible
aquifers to determine how USDWs were identified and discussed in
the CCA. The EPA also examined whether the flow rates and
directions were included in the description. The modeling
assumptions and specifications for the bounding analysis were
examined to assess reliability and assurance of safety. The
EPA reviewed the estimated concentrations of radionuclides to
determine if they complied with the groundwater protection
standard (see the CCA Compliance Application Review Document [CARD] 53, U.S. Environmental Protection Agency 1998, for details of the EPA’s CCA
review).

The EPA found that the DOE’s determination
of the USDWs was in accordance with definitions contained in section 191.22 and with the compliance
criteria in section 194.53. The
bounding analysis was performed with conservative assumptions for
a hypothetical USDW to estimate contamination and potential doses
to a receptor.

The DOE monitored and evaluated new wells drilled
in the area since the completion of the CCA. A new well,
C-2737, was drilled to replace H-1 in 2001. Water sampled
from the Dewey Lake Formation showed 2,590 ppm TDS.
Additional wells were drilled at the WIPP site to investigate the
extent of groundwater at the contact of the Santa Rosa and Dewey
Lake Formations. The groundwater samples indicate TDS at
both below and above 10,000 ppm TDS. The DOE was unable to
pump water from any one of these boreholes at a rate of 5 gpm or
more.

The updates and changes made by the DOE in the
CRA-2004 did not significantly impact the conclusions regarding
USDWs in the CCA. In the CRA-2004, the DOE continued to
identify the Culebra, Dewey Lake, and Santa Rosa as the only
potential USDWs. The DOE stated that the conservative
bounding analysis used for the 1998 Certification Decision
compliance assessment was still applicable (see the CRA-2004,
Chapter 8.0, Section 8.2.1.1).

The EPA evaluated the information on the USDWs
contained in the CRA-2004, Chapter 8.0 and examined data from the new wells drilled within the
study area since the 1998 Certification Decision. The EPA
determined that the DOE applied adequately conservative
assumptions to the data for a hypothetical USDW to determine
compliance with section 194.53.

Because of the lack of significant changes to the
parameters for the protected individual, the potential exposure
pathways, and the USDWs, the EPA agreed that the bounding
analysis performed for the dose calculation in the CCA still
applied. See CRA-2004 CARD 55 (U.S. Environmental Protection Agency 2006) for more information on
the results of the compliance assessment.

The EPA received no public comments on the
DOE’s continued compliance with the consideration of USDW
requirements in section 194.53.

Based on a review and evaluation of the CRA-2004
and supplemental information provided by the DOE, the EPA
determined that the DOE continued to comply with the requirements
of section 194.53.

1.
Updated information regarding average household water consumption
in communities near the WIPP has been obtained from the New
Mexico Office of the State Engineer to assess the continued
appropriateness of criteria for making USDW determinations.
The updated information is included in Appendix
IGP-2009, Section IGP-3.1.1. A review of these new data
indicates that no change in the criteria for making USDW
determinations is warranted.

2.
Several new boreholes have been drilled near the WIPP since
the CRA-2004. These include wells to further characterize
flow characteristics in the Culebra and to better understand
shallow groundwater flow near the WIPP salt storage piles.
Detail regarding these new wells is included in Appendix
IGP-2009, Section IGP-3.2. Data from these wells
indicate that no changes to the previous USDW determinations are
warranted.

3.
Based on the review of available data in support of the CRA-2009,
the DOE concludes that no modification of the USDW determinations
reported in the CCA, Chapter 8.0 and Appendix USDW
is warranted (see Appendix IGP-2009, Section IGP-3.2). The
DOE continues to conclude that USDWs are present in the Culebra,
and potential USDWs are present in the Dewey Lake and the Santa
Rosa. Based on this, the DOE concludes that all USDWs in
the accessible environment expected to be affected by the
disposal system over the regulatory time frame have been
considered. In addition, the DOE approach ensures
that underground interconnections among bodies of surface water,
groundwater, and USDWs are considered.

Based on these considerations, the DOE believes
that continued compliance with the provisions of section 194.53 is demonstrated.